Re: [LEDE-DEV] [PATCH] imx6: disable dma on uart

[Bas Mevissen]

On 02/22/2018 12:20 PM, Koen Vandeputte wrote:
> When this target got updated to 4.14, this patch got removed to
> re-evaluate if it was still needed.
> 
> Extensive testing now shows this issue is still present.
> Let's re-add the patch to fix it for now.
> 
> As the uart bus is very low bandwidth .. performance impact is negligible.
> 
> Boot log:
> 
> [   22.513051] imx-uart 202.serial: DMA transaction error.
> [   22.522721] imx-uart 202.serial: DMA transaction error.
> 

An alternative solution is to add the following to the uart's device
tree definition:

dma-names = "", "";

e.g.

 {
pinctrl-names = "default";
pinctrl-0 = <_uart1>;
dma-names = "", "";
status = "okay";
};

Regards,

Bas.




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Re: [LEDE-DEV] [PATCH] imx6: disable dma on uart

[Felix Fietkau]

On 2018-03-08 11:00, Koen Vandeputte wrote:
> 
> 
> On 2018-02-22 12:44, Felix Fietkau wrote:
>> On 2018-02-22 12:20, Koen Vandeputte wrote:
>>> When this target got updated to 4.14, this patch got removed to
>>> re-evaluate if it was still needed.
>>>
>>> Extensive testing now shows this issue is still present.
>>> Let's re-add the patch to fix it for now.
>>>
>>> As the uart bus is very low bandwidth .. performance impact is negligible.
>>>
>>> Boot log:
>>>
>>> [   22.513051] imx-uart 202.serial: DMA transaction error.
>>> [   22.522721] imx-uart 202.serial: DMA transaction error.
>>>
>>> As a sidenote:
>>> The patch mentiones an issue with RS485, but the bootlog
>>> errors above were recorded with the uart ports in standard RS232 mode.
>>>
>>> Compile/Run-tested on imx6/GW5200
>>>
>>> Signed-off-by: Koen Vandeputte 
>> Could you please also report this issue upstream and send a patch that
>> makes it possible to disable DMA via DT and/or kconfig?
> Bugreport was filed some time ago [1]
> No response so far ..
Did you send it to the relevant mailing lists as well?

- Felix

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Re: [LEDE-DEV] [PATCH] imx6: disable dma on uart

[Koen Vandeputte]

On 2018-02-22 12:44, Felix Fietkau wrote:

On 2018-02-22 12:20, Koen Vandeputte wrote:

When this target got updated to 4.14, this patch got removed to
re-evaluate if it was still needed.

Extensive testing now shows this issue is still present.
Let's re-add the patch to fix it for now.

As the uart bus is very low bandwidth .. performance impact is negligible.

Boot log:

[   22.513051] imx-uart 202.serial: DMA transaction error.
[   22.522721] imx-uart 202.serial: DMA transaction error.

As a sidenote:
The patch mentiones an issue with RS485, but the bootlog
errors above were recorded with the uart ports in standard RS232 mode.

Compile/Run-tested on imx6/GW5200

Signed-off-by: Koen Vandeputte 

Could you please also report this issue upstream and send a patch that
makes it possible to disable DMA via DT and/or kconfig?

Bugreport was filed some time ago [1]
No response so far ..

Thanks,

- Felix



[1] https://bugzilla.kernel.org/show_bug.cgi?id=198889

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[LEDE-DEV] [PATCH] imx6: disable dma on uart

[Koen Vandeputte]

When this target got updated to 4.14, this patch got removed to
re-evaluate if it was still needed.

Extensive testing now shows this issue is still present.
Let's re-add the patch to fix it for now.

As the uart bus is very low bandwidth .. performance impact is negligible.

Boot log:

[   22.513051] imx-uart 202.serial: DMA transaction error.
[   22.522721] imx-uart 202.serial: DMA transaction error.

As a sidenote:
The patch mentiones an issue with RS485, but the bootlog
errors above were recorded with the uart ports in standard RS232 mode.

Compile/Run-tested on imx6/GW5200

Signed-off-by: Koen Vandeputte 
---
 .../imx6/patches-4.14/210-disable-uart-dma.patch   | 23 ++
 1 file changed, 23 insertions(+)
 create mode 100644 target/linux/imx6/patches-4.14/210-disable-uart-dma.patch

diff --git a/target/linux/imx6/patches-4.14/210-disable-uart-dma.patch 
b/target/linux/imx6/patches-4.14/210-disable-uart-dma.patch
new file mode 100644
index ..6abbb9330188
--- /dev/null
+++ b/target/linux/imx6/patches-4.14/210-disable-uart-dma.patch
@@ -0,0 +1,23 @@
+Based on following upstream patch by Tim Harvey (Gateworks):
+
+https://github.com/Gateworks/openwrt/commit/80a01b6582f94c4547f39d3a25e0a1e9b6eb9877
+
+TX complete DMA messages are getting missed.
+This is also currently an issue in mainline.
+For now we will disable DMA in serial/imx.c.
+
+This resolves an issue encountered with RS485 transmit.
+
+--- a/drivers/tty/serial/imx.c
 b/drivers/tty/serial/imx.c
+@@ -1268,10 +1268,6 @@ static int imx_startup(struct uart_port
+ 
+   writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
+ 
+-  /* Can we enable the DMA support? */
+-  if (!uart_console(port) && !sport->dma_is_inited)
+-  imx_uart_dma_init(sport);
+-
+   spin_lock_irqsave(>port.lock, flags);
+   /* Reset fifo's and state machines */
+   i = 100;
-- 
2.7.4


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